Development of images



United States Patent O Mice 3,410,686 DEVELOPMENT OF IMAGES Merle P. Prater, Vestal, N.Y., assgnor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed June 30, 1964, Ser. No. 379,164 2 Claims. (Cl. 9649) ABSTRACT OF THE DISCLOSURE A method for the selective development of images in light-sensitive, thermally developable diazotype compositions of either the vesicular or color-forming type by placing an electric charge corresponding to the desired image on the surface of the diazotype element, adhering oppositely charged, infra-red absorbing toner particles to the electric charge pattern and exposing the element to infrared radiation to selectively heat the toner particles thereby developing the image.

The present invention relates to a method for the selective development of images on copying materials, such as thermally developable film, copying papers or the like.

There are a number of wellknown systems for the production of vesicular or colored images through the use of light-sensitive diazotype compositions. Vesicular materials are ordinarily developed by selective exposure to ultravioletlight followed by heating. Certain other diazonium formulations may be developed by heat to give colored or dye images. The present invention provides a new method for the development of elements comprising thermally developable diazotype compositions of either the vesicular or color-forming type.

The. invention will be more fully appreciated in view of the following description considered in the light of the accompanying drawing.

In the drawing:

FIGURES la through 1f are cross-sectional, edge views of thermally developable diazotype elements having a high dielectric surface during various stages of development to form a vesicular image in accordance with the present method, and

FIGURES 2a through 2f are crosssectional, edge views of thermally developable diazotype elements having a high dielectric surface during various stages of development toform a colored image in accordance with the present invention.

In accordance with the present invention, thermal diazotype compositions incorporated in films, copying papers or like elements, are selectively developed by first forming on the surface of the element an electrically charged pattern corresponding to the desired image. The electrically charged pattern may be produced in a number of ways, `such as by charge transfer from a photo-conductor, by impinging with an electron beam, or by applying a charged stylus tothe surface of the element.

Next, where the thermal diazotype element is of the type which yields as vesicular image, the entire surface of the element is exposed to ultraviolet radiation. The lightsensitive diazotype compound in the element is decomposed by the ultraviolet radiation to yield nitrogen, as small nucleating centers, which remains entrapped in the film.

The element is then coated with high melting point infra-red absorbing toner particles which have an electrical charge opposite to the charge of the pattern on the surface of the element. The infra-red absorbing toner 3,410,686 Patented Nov. 12, 1968 particles may be applied by any well-known technique, such as cascading, fur brush, magnetic brush, powder cloud, etc. These particles adhere to the surface of the film at those points where the oppositely, electrically charged pattern is present. The excess toner is carried away from the uncharged portions of the surface by the toner applicator.

The element, bearing the toner particles in the form of an image pattern, is then exposed to infra-red radiation which efficiently imparts point sources of heat to the film underneath the toner particles. The heat causes the nitrogen gas in the nucleating centers to expand and develop an image corresponding to the chargedv and toned pattern.

The unmelted toner particles are then removed from the surface of the film for reuse, if required. The removal of the infra-red absorbing toner on the surface is accom plished by brushing, vacuuming, or cascading of carrier beads.

In developing a vesicular image, it is important that the steps of ultraviolet radiation, electrostatic image establishment, toning and exposure to infra-red radiation be carried out in farily rapid succession so that the nitrogen initially produced upon ultraviolet exposure can be developed to form a vesicular image before it diffuses out of the element.

In the case of a thermal diazotype element of the type which may be developed to produce a colored image, the steps are quite similar, but they are carried out in a slightly different sequence.

The first step of the method comprises the formation on the surface of the diazotype element of a charged pattern corresponding to the desired image. In this case, however, toner particles, having an electrical charge opposite to that of the charged pattern, are next applied to the element to form a pattern of infra-red absorbing toner particles adhered to the electrically charged pattern.

The element coated with a patterned layer of the electrically charged and infra-red absorbing particles is then exposed to ultraviolet light to decompose the lightsensitive diazotype compound in those areas of the film not masked or screened by the toner particles.

The element is then exposed to infra-red radiation. The presence of the infra-red -absorbing particles causes the areas of the diazotype element underneath the particles to be heated selectively to a temperature at which the thermal diazotype composition is developed.

At this point, the development of the image could also be effected by brushing off the toner and applying conventional alkaline developing uids to the surface of the element. Most thermally developable diazotype elements are also capable of alkaline development in this manner.

As a nal step, the unmelted toner particles are removed from the surface of the film.

Thus, it will be seen that the present invention is particularly useful in that it allows a much more efficient use of heat sources in the thermal development of images. As a consequence, machines using the present method may be made smaller and more compact and may more easily be kept at ambient temperature, thus lessening the need for ventilation and cooling of the device.

Considering the invention in more detail and referring to the drawings, it will -be seen that in FIGURE 1a, the starting element 10 comprises a substrate 11 coated on one surface with a film 12 of a light-sensitive diazotype composition. The element could also be in the form of a self-supporting `film containing the diazotype compounds. Elements capable of forming vesicular images through the decomposition of diazotype compounds t yield IHUO gen and subsequent heating are well known in the art. For example, the materials described in U.S. Patent 3,032,414, James et al., issued May 1, 1962, and a number lof other issued patents, may be used in the present invention.

The surface of film 12 is then charged with an electrically conductive pattern 13 corresponding to'the desired image. As noted, this .pattern can be produced in any conventional manner, such as by transfer from a photoconductor, by impinging an electron ibeam on the surface, or by use of a charged stylus. The charged pattern may be an original, may ybe taken from another original, or may be enlarged or reduced from another film transparency, thus forming a copy.

As will be seen in FIGURE 1c., the element 10, provided with charge pattern 13, is then exposed uniformly to ultraviolet radiation which interacts with the lightsensitive diazotype compound and produces nitrogen. Of course, yother photo-sensitive gas producing compounds, besides diazotype materials, may also be developed in this manner.

The nucleating centers 0f gas, such as nitrogen, within film 12 are indicated `by small dots 14. Nucleating centers 114 constitute the basis for the development of the vesicular image.

It will be apparent that the `order of the second and third steps, that is, the application of the charged pattern and the uniform exposure to ultraviolet light, may be reversed.

After exposure to ultraviolet light, the charged surface of the film is dusted with infra-red absorbing, high melting point toner particles 15 which have a trieboelectric charge which is opposite to that of the electrically charged pattern. As seen in FIGURE 1d, due to th opposite charges, the toner particles are attracted to and adhere to the electrically charged pattern. The excess particles are carried away from the uncharged portions of the surface of film 12 by the toner carrier or applicator. This results in the formation of a toner pattern on top of the electrically charged pattern. Suitable toner particles include caribou black, or any commercial toners, such as Xerox 939, having a melting point sufficiently high to cause nucleating center development without fusing to the surface of the film.

As shown in FIGURE 1e, the element is then exposed to infra-red radiation (indicated by arrows) which selectively heats the regions coated with the infra-red absorbing particles to a temperature which results in rapid expansion of the underlying nitrogen nucleating centers 14 to form larger cells 16. Cells 16 result in the scattering of light passing through the Ifilm and provide an image corresponding to the superimposed toner patterns.

The heating of the untoned areas is kept to a low temperature so that bubbles or light-scattering centers are not formed in those portions of the film. Nitrogen or Ether gas in those areas then gradually diffuses out of the The toner particles are then removed from the surface of the film leaving the substrate 11, the surface diazotype film 12 and a vesicular image 16 corresponding to the original charge pattern 13. The removal of the toner particles may 'be accomplished hy brushing, vacuuming or cascading glass beads in a reverse trieboelectric pickup.

Turning now to the process for the production of dye images according to the invention and considering the features of the process in more detail, it will be seen in FIGURE 2a that the initial element 20 may comprise a color-forming thermal diazotype film 22 coated on a substrate 21. Thermal diazotype compositions which are developable by heat to produce colored images are well known in the art. Examples of thermally developable diazotype materials are described in copending U.S. patent applications, S/N 325,171, now Patent No. 3,307,952, and S/N 325,l55, now Patent No. 3,303,028 of Claude Aebi, assigned to the assignee of the present application, as well as in numerous issued patents. u

The thermal diazotype element 20 is provided with an electrically charged pattern 23 corresponding to the desired image. This may be done in the same manner as was done in developing vesicular images as previously described, and results in an element having a charged surface as Shown in FIGURE 2b.

As shown in FIGURE 2c, the charged element 20 is then brushed or cascaded ywith toner particles 24 which have a trieboelectric electric charge opposite to the charge of the pattern 23 carried on the surface of film 22. No toner particles will remain in the uncharged portions of film 22 because there is no charge to remove or attract the toner from the toner carrier or applicator.

As shown in FIGURE 2d, the element 20 is then exposed to ultra-violet light (indicated by arrows) to decompose the thermal diazotype compound in film 22 in those areas 25 which are not screened by toner particles 214.

Referring to FIGURE 2e, the element is next eX- posed to infra-red radiation (indicated yby airows). The particles absorb the infra-red energy and create point sources of heat which is transferred to the unexposed sections of film 22 underneath the toner particles. This results in the development of an image 26 by color-forming reaction of the thermal diazotype composition in film 22.

As previously noted, the image 26 may also be developed at this point by treating the element with an alkaline developing fluid, such as aqueous ammonia or ammonia gas.

As shown in FIGURE 2f, the infra-red absorbing toner particles may then be removed from the surface of film 22, leaving the thermal diazotype image 26 which corresponds to the original electrically charged pattern 23.

The above-described invention will be more fully appreciated in the light of the following examples.

Example 1 A polyethylene terephthalate substrate is coated with a film of a diazotype material having the following composition:

Functiou Component Parts by Weight Resinous Vehicle Saran F- 10, 0 Diazo Sensitizer Edwal Compound #8 1.0 Solvent Methyl Ethyl Ketone. 30.0 Do Methyl Alcohol 8.0 The composition is coated and dried 0n the substrate and surface of the resulting diazotype film is then provided with an electrical charge according to a pattern which corresponds to the desired image. This charge pattern is applied by charge transfer from an amorphous selenium photo-conductor surface containing the latent electrostatic image pattern desired.

The surface of the charged element is then flooded with ultraviolet light between 3400 A. and 4400 A. at an energy level of approximately .4 watt second/cm.2 which results in the decomposition of the light-sensitive diazonium sensitizer compound yielding nitrogen nucleating centers.

Finely divided infra-red sensitive, high melting point, carbon black toner particles, having a particle diameter in the range of from about 0.5 to 5.0 microns, are trieboelectrically charged opposite to the charge on the surface of the film. The charged infra-red absorbing toner particles and carrier are then brushed over the surface of the element and adhere to the surface where the pattern of opposite electrical charge is present. The surface of the element with toned image is then exposed to infrared radiation for a few seconds to raise the temperature of the infra-red absorbing particles to about "-190" F The infra-red the surface. As

absorbing particles are then brushed from the result of this development, a vesicular 6 image iS formed in the flrn which has the Same Coneuraexposing the entire element to ultraviolet radiation to [1011 3S the Orlgllal e1etf1a11y Charged Pattern form nitrogen nucleating centers in said element,

Example 2 substantially.immediately adhering toner particles to said electrically charged pattern, said toner particles A polyethylene terePhthala/ Support 1S coated WM) a 5 comprising infra-red absorbing material having an thermal developable diazotype Ematerial of the following electrical charge Opposite to the Charge of said pat composition: tem, and

Function Componcnt Pal-@S by exposing said element to infra-red lradiation to heat Welght selectively said infra-red absorbing particles and minzs gmconiaxad 1g 10 timsmit heatd selectively if; Said element, theeby n -Ol Bry-M 10mmn e ecting rapi expansion o said nitrogen nuc eat- Llght Sensmve Dmc p Zzrinuollillillilillmme- 1 ing centers to form an image comprising light-diffusgopef 3d7dgtnglhtha1en-- l; ing enlarged cells within said element, and svniii...:1131111121132:Mtlami 11.113113: ,o removing said toner particles from said element.

2. A method for forming an image in a thermally .The surface of. .the.resutlng Cqatmg Pf the thermal developable, light-sensitive diazotype element capable of dlazotype composition 1S then provlded Wlth an electrical undergoing a color-forming reaction at elevated temperacharge by Sannmg an electron beam OVfar the Surfac of tures, said element comprising a light-sensitive layer, said the coating in a vacuum to trace the outline of the desired layer comprising a diaz() compound and an azo coup1ing image' 20 component, consisting essentially of the steps of: Nexf" the charged Surface 1S.cascadefi Wlth hlgh melt providing an electrically charged pattern on the surface ing point Xerox 939 toner particles which have a charge of Said element, opposite 10 the,e1ectr1ca l charge of th? Patten? on the adhering toner particles to said electrically charged surface of the diazo coating. These particles are infra-red pattern, said toner particles comprising infra red absorbing and adhere to the Surfaoe of the dlazolype absorbing material having an electrical charge oppofilm at those places where the electrically and oppositely site to the Charge of Said pattern, Charged Pattern 1S Present' exposing said element to ultraviolet light to decompose The element is then exposed .to ultraviolet light which the 1ight sensitive diazotype compound in said mep decomposes the light-sensitive diazotype compound in all many developable diazotype element in those areas areas not screened or masked by the opaque toner parexposed to the ultraviolet light and ticles. Next, the element is exposed to infra-red radiation exposing Said element to infrared radiation to heat Whloh 1S a'bsorbed by toe toner parool provlomg high selectively said infra-red absorbing toner particles local heatmg offfho dlazotype lm ,beneath the toner and transmit heat selectively to said element to pattern. The heating is continued to raise the temperature develop the diazotype element in ,hose areas which of the lmfo' about 159i C- to deYeloP a Colored Image 35 are adjacent to the infra-red absorbing particles and corresponding to the original electrically charged pattern. which contain undecomposed diazotype composition I t Wu bo apparent tojlhose Skilled 1n the art that capable of undergoing a colorforming reaction, and various vesicular compositions and color-forming diaremoving said toner particles from Said element zonium compositions may be substituted for those del scribed above. Likewise, other infrared absorbing toner 40 References Cited particles may be employed with equal success. However, such modifications and changes and many other variations UNITED STATES PATENTS may be made in the present method without departing 3,226,227 12/ 1965 Wolff 96-1.8 from the spirit or scope of the invention as expressed in 2,911,299 11/ 1959 Bflfll et al. 96-49 the following claims. 2,916,622 12/1959 NleSSt 250-65.1 What is claimed is: 2,939,787 6/1960 Gialrio 96-1 1. A ymethod for forming an image in a thermally 3,113,022 12/1963 CaSSlerS etal. 96-91 X developable, light-sensitive diazotype element capable of 3,189,455 6/1965 DaeCh 96-49 X yielding a vesicular image, said element comprising a 3,194,659 7/ 1965 BituS et al 96-49X light-sensitive layer, said layer comprising a resinous 3,224,354 12/1965 DIZ-gell et al 96-49 X vehicle and a diazo compound, consisting essentially of 3,224,878 12/ 1965 KllmkOWSki et al. 96-49 the steps of:

providing the surface of said element with an electri- NORMAN TORCHIN Pmay Examinercally charged pattern corresponding in configuration C. L. BOWERS, JR., Assistant Examiner. to the desired image, 

